The present invention relates to the conversion of a free-space microwave radiation signal to a lower frequency signal. More particularly, the present invention relates to a device for converting a microwave signal to an intermediate frequency signal for subsequent receiver processing by mixing the incoming microwave signal with a local oscillator signal.
In prior art microwave receiving apparatus, a radio frequency (RF) signal is received by an antenna. The signal produced by conversion of a plane wave signal is transmitted over a waveguide to a separate device for mixing the signal with a local oscillator signal to produce an intermediate frequency signal. In early microwave apparatus, horn-type antennas and waveguides were utilized. The resulting structure was physically large and bulky.
The problem of size in microwave reception apparatus has been overcome to some extent by the utilization in modern microwave reception apparatus of microstrip-type antennas and stripline or microstrip transmission lines. However, receivers built to intercept a free-space wave and convert it to a lower frequency signal continue to require separate, interconnected antenna and mixer structures. Also, the cost of the assembling of conventional antenna-waveguide-mixer apparatus is quite expensive.